Image sensors are of ten embodied by a plurality of photo sensitive pixels. Each pixel receives information indicative of a portion of the image. The information is in the form of incoming photocarriers indicative of the incoming light photons. Each pixel accumulates photocarriers indicative of the amount of light impinging on that pixel. That amount of time is often called the exposure.
The present invention describes varying the pixel exposure by varying the time between enabling the pixel to integrate and reading the pixel. The pixels are formed into an array of pixels. Two counters are used to address the array. One counter, called the shutter pointer, keeps track of the address of the pixels that will next be enabled. Once enabled, those pixels will begin to integrate. The other counter called the read counter keeps track of the row address to be read. The time between enabling and reading determines the exposure.
For any given exposure, the difference between these two counters is always the same. Each pixel in the array hence gets the same amount of exposure, thereby avoiding one portion of the image having a different look than another.
The exposure can be changed by an automatic exposure technique or by manual input from the user. The change of exposure changes the difference between the enable and read addresses.
One aspect is to change this exposure using a seamless technique in which no one image/field has internally-varying characteristics. This is done without changing the frame rate or diffusing the exposure difference for pixels within the same frame.
Another aspect uses a third counter to look ahead to the next frame while the read pointer and shutter are processing the current frame. This third counter evaluates the program exposure at the start of a new frame. When the exposure changes, the third counter is advanced to the next frame. The current frame with the old exposure is simultaneously processed.